Aquatic Toxicology 70 (2004) 63–81
Physiological action of dissolved organic matter in rainbow trout in
the presence and absence of copper: Sodium uptake kinetics and
unidirectional flux rates in hard and softwater
Aline Y.O. Matsuo
a,b,∗
, Richard C. Playle
c
, Adalberto L. Val
a
, Chris M. Wood
b
a
Laboratory of Ecophysiology and Molecular Evolution, Instituto Nacional de Pesquisas da Amazˆ onia (INPA),
Alameda Cosme Ferreira, 1756 – Aleixo, 69083-000, Manaus, AM, Brazil
b
Department of Biology, McMaster University, 1280 Main Street West, Hamilton, ON, Canada L8S 4K1
c
Department of Biology, Wilfrid Laurier University, Waterloo, ON, Canada N2L 3C5
Received 9 March 2004; received in revised form 6 July 2004; accepted 19 July 2004
Abstract
We investigated the physiological effects of dissolved organic matter (DOM) on sodium (Na
+
) transport in juvenile On-
corhynchus mykiss (∼2.5 g) in the presence and absence of simultaneous acute exposure to copper (Cu
2+
; 0, 70, and 300 gl
-1
).
Trout were acclimated in either hardwater (∼1000 M Ca
2+
) or softwater (∼100 M Ca
2+
), and DOM was tested at approx-
imately 8 mg C l
-1
using a natural (NOM) and a commercial (AHA) source. Ion transport was evaluated based on kinetics
estimates (maximum Na
+
uptake rates, J
max
; substrate affinity, K
m
) and unidirectional flux measurements (J
in
, J
out
, J
net
). J
max
was higher and unidirectional flux rates were greater in softwater-acclimated trout. Fish exposed to DOM alone in hardwater
exhibited an increased Na
+
transport capacity indicated by both the kinetics (67% higher J
max
for AHA) and J
in
measurements
(153% higher for AHA and 125% higher for NOM). In softwater, the effects of DOM alone on kinetic parameters and unidirec-
tional flux rates were negligible. Cu
2+
affected Na
+
uptake by a mixed-type inhibition (both non-competitive and competitive).
In hardwater, only K
m
was increased (i.e., affinity decreased), whereas in softwater, K
m
was increased and J
max
was decreased,
with more marked effects at the higher Cu
2+
level. In hardwater, the stimulatory effect of AHA on J
max
persisted even in the
presence of 300 gl
-1
Cu
2+
, whereas both AHA and NOM prevented the increase in K
m
caused by Cu
2+
; these effects were
reflected in J
in
measurements. In softwater, AHA helped to protect against the increased K
m
caused by high Cu
2+
, but there was
no protection against the inhibition of J
max
. Unidirectional flux measurements indicated that in softwater, Cu
2+
inhibited J
in
at
70 gl
-1
, whereas at 300 gl
-1
Cu
2+
, J
out
was also stimulated. Fish were more affected by Cu
2+
in softwater, as indicated by
the inability to control diffusive losses of Na
+
and a reduced ability to take up Na
+
, but in the presence of DOM, losses were
© 2004 Elsevier B.V. All rights reserved.
∗
Corresponding author. Tel.: +55 92 643 3187; fax: +55 92 643 3186.
E-mail address: matsuoaline@aol.com (A.Y.O. Matsuo).
0166-445X/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.aquatox.2004.07.005